Don't do it.

As an experiment, put a string of LED's across your Car Battery without any form of Current Limiting - that's a reasonably constant voltage - then go rev your car engine up...

> Could i use 4 diodes to make a rectifier?

Yes

> The diodes are only meant for about 50V 1A.

Well that's kinda stupid to use them on 240v then!

> I found one thats 470N 250V. Would 470N be enough?

Depends on how much current you're pulling... but the 250v bit is totally inadequate, because by the time you full-wave rectify mains you'll have close to 340vDC.

Back to my first line... DON'T DO IT. You are running the risk of harming yourself, your property and putting at serious risk those around you.